This invention relates in general to handling apparatus for electronic devices. More specifically, it relates to a magnetic system for storing devices with axial, magnetically permeable leads, particularly electrically polarized devices such as diodes.
In the manufacture of electronic devices it is necessary to test the devices and sort them according to whether they are defective or according to the value of some parameter. The sorted devices are collected in bins. Production economics require that these testing, sorting and collecting operations be very rapid, reliable and without significant interruption.
Certain devices such as axial lead diodes present special problems. Diodes are electrically polarized, but they typically have a symmetrical configuration so that it is impossible to visually determine which lead is "positive" and which lead is "negative". It is therefore necessary in their manufacture to identify one lead, e.g. the positive side of the diode, and maintain that identity. This is usually done by maintaining a correlation between the polarity and the spatial orientation of the device.
Handling problems of axial lead diodes and similar devices are compounded by the configuration of the devices and their variability. The long, thin leads are easily bent. Both the overall length and the mass of the devices vary. The storage system must not damage the devices and must accommodate these variations. In sorting apparatus where testing is performed on a rotating table and the tested devices are fed to a linear array of collecting bins below the table, variations in the mass of the different devices can result in appreciable variations in the input momentum of the device to the storage system. Also, both the vertical and the horizontal angles of approach of the devices to the bin will vary from bin to bin.
U.S. Pat. Nos. 2,975,878; 3,231,133; and 3,450,259, all assigned to the Hughes Aircraft Co., describe a system for handling, testing, sorting and classifying axial lead, electrically polarized devices. A hopper feeds devices downwardly to a vertical, double track system described in the '878 patent. One track with a spiral groove introduces a 180.degree. rotation in devices that are sensed as having an orientation opposite to those directed down the other track, which introduces no rotation. A mechanical escapement mechanism described in the '133 patent feeds the devices from the track system to an endless belt or track described in the '259 patent. The belt carries the devices to a test station. Depending on the result of the test, an electromagnet may be activated to pull the tested device to a selected storage box, e.g. one for defective devices. In another form, the escapement mechanism feeds the devices directly to a test station adjacent a permanent magnet and a pair of electromagnets control movement of the device along one of three paths to an associated storage box. In either form, the movement of the devices through the system is lateral, that is in a direction perpendicular to the leads.
U.S. Pat. Nos. 3,581,889 and 3,537,580, both assigned to Western Electric Co., describe another system for handling, testing, sorting and storing axial lead, but unpolarized, devices. The '580 patent describes an input bin that orients a random collection of the devices placed at one end in a magnetic field generated by a pair of spaced apart, mutually inclined magnets. The inclination creates a variation of the intensity of magnetic field that urges the devices laterally toward the opposite end of the bin where they are picked off by a magnetic carrier wheel. The wheel rotates the devices under a test station. Electronic circuitry correlates the test results with the action of a blade or electromagnet that strips the devices from the wheel to a sorting device. The '889 patent, describes a horizontal wheel that rotates the devices to one of a succession of chutes that lead to associated storage bins. Circuitry correlates the test results with a specified chute and bin. The devices are removed by energization of an electromagnet and an airflow. This system has no capability to process polarized devices and maintain them in a spatial orientation indicative of their polarity.
While these systems use magnetic fields to control the movement of axial lead devices, there is little teaching with respect to the problems of the output or storage end of the system. Moreover, only the Hughes system deals with polarized devices, and it requires a relatively complex arrangement to orient, advance and process the devices in a manner that retains their polarity-indicating spatial orientation. None of the aforementioned patents address the problem of handling, sorting, and laterally storing polarized axial lead devices that are advancing initially in an axial mode without losing an initial polarity indicating orientation.
It is therefore a principal object of this invention to provide a magnetic system for storing polarized axial lead devices entering the system in an axial mode where the system maintains a correlation between the electrical polarization and the spatial orientation of the device.
Another object is to provide such a storage system that operates effectively for devices having different dimensions, input momenta, and input angles to the system.
A further object is to provide a storage system that provides a readily visible and foolproof arrangement for maintaining the polarization/orientation correlation.
Yet another object is to provide a storage system that allows the replacement of cassettes without interrupting preceeding operations and is highly compact.
A still further object is to provide a storage system with the foregoing advantages that does not damage the devices.
Another object is to provide a storage system that is rapid, reliable, and sufficiently uncomplicated to provide low maintenance requirements and a comparatively low cost of manufacture.